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sched: Fix possible divide by zero in avg_atom() calculation

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proc_sched_show_task() does:

  if (nr_switches)
	do_div(avg_atom, nr_switches);

nr_switches is unsigned long and do_div truncates it to 32 bits, which
means it can test non-zero on e.g. x86-64 and be truncated to zero for
division.

Fix the problem by using div64_ul() instead.

As a side effect calculations of avg_atom for big nr_switches are now correct.

Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1402750809-31991-1-git-send-email-mguzik@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mateusz Guzik 2014-06-14 15:00:09 +02:00 committed by Ingo Molnar
parent b6220ad66b
commit b0ab99e773
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/debug.c
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@ -608,7 +608,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
avg_atom = p->se.sum_exec_runtime;
if (nr_switches)
do_div(avg_atom, nr_switches);
avg_atom = div64_ul(avg_atom, nr_switches);
else
avg_atom = -1LL;